I just want to say that I really appreciated this kata, as it gave me an opportunity to learn a JavaScript feature that I wasn't already familiar with. I use stream functions all the time in my Node development work, but I have never really thought about how to generate them before. Very satisfying to put it together.

Whenever I run into this problem, I just add a log statement in the function that will show me what the value is from the test. For JavaScript, this was:

log.debug(phoneNumber);

Attempt to pass again and you will see the test value along with the pass/fail response.